This is a feasibility study to demonstrate Yohimbine or procaine induced activation of limbic structures (ventral prefrontal cortex and amygdala) using fMRI on a conventional 1.5T scanner in parallel with 150 PET studies and to use FDG PET to confirm that any limbic activation documented with fMRI or 150 is due to changes in neuronal metabolism rather than direct effects of Yohimbine or procaine on blood flow.